Fig. 3.

Diagram showing the periosteal and endosteal Pagetic osseous mechanisms involving the cortex of the spinal canal resulting in spinal canal narrowing. Normal cortical thickness (orange) of the spinal canal (white) is depicted at the top. a Expansion of bone due to periosteal apposition/endosteal resorption results in a thin cortical outline (solid black arrow) of the narrowed spinal canal (dashed arrow). b Bony expansion due to periosteal apposition/endosteal apposition results in a thickened cortical outline (solid black arrow) of the narrowed spinal canal (dashed arrow)